Olefinic polymerization in the presence of fluorine compounds



Patented Jan. 17, 1950 OLEFINIC POLYMERIZATION IN THE PRIES- ENCE FFLUORINE COMPOUNDS John S. Saylor, J12, Reading, Pa, assignor toStandard Oil Development Company, a corporation of Delaware No Drawing.Application September 30, 1944, Serial No. 556,658

4 Claims. i This invention relates to the low temperature polymerizationof olefinic materials and relates particularly to the polymerization atlow temperature in the presence of a fugitive solid to provide agrinding action, such as a pulverizing refrigerant; and a diluent.

This application is a continuation-in-part of my co-pending applicationSerial No. 502,438, filed September 15, 1943, now abandoned, for"Improved low temperature polymerization process 1 It has been foundpossible to polymerize olefins such as isobutylene in admixture with apolyolefin such as butadiene or isoprene or the like attemperaturesranging from -20 C. to -100 C. or even as low as -164 C. bythe application thereto of a Friedel-Crafts catalyst, preferably insolution in a low-freezing, non-complex-forming solvent to yield ahighly valuable synthetic substitute for rubber. However, the reactionis difficult to control and dimcult to conduct because of the thick,heavy, gummy character of the polymer both at the low temperature ofpolymerization and at room temperature; and great diillculty has beenencountered in developing a process which was both simple to operate andat the same time yielded a high grade polymer.

The present invention is based upon the discovery that if thepolymerization is conducted in a kneader in the presence of a fugitivesolid, a solid refrigerant such as solid carbon dioxide, the polymer isbroken up into fragments by the grinding action between the blades andthe fugitive solid, which fragments can be handled with reasonablesatisfaction; and the further discovery that if the polymerization isconducted both in the presence of a solid refrigerant to break up thepolymers and a diluent such asmethyl chloride or liquid propane or thelike to maintain the slurry, the new and unexpected phenomenon appearsthat when the resulting polymer is cured, it gives a very much higherpure gum tensile strength, and better physical properties generally thanare otherwise obtainable.

Thus, the invention provides a new and useful combination of membersutilizing a kneader as the reaction vessel; ut lizing the interactionbetween the kneader blades and a solid refrigerant or volatile solid inthe kneader upon the olefinic polymerizable material; and a diluent bywhich a very much superior polymer is obtained because of the improvedpolymerization conditions, and the fact that the polymer is maintainedas a fine grained slurry during the entire polymerization reaction.Other objects and details of the invention will be apparent from thefollowing description.

In practicing the invention, a kneader of the general character of theso-called Werner- Pfieiderer" type is used. This kneader is charged witha fugitive solid which is preferably a solid refrigerant, such as solidcarbon dioxide or other low melting solid which may be itself arefrigerant or may melt or volatilize at a temperature near to thepolymerization temperature. Such a substance as solid methyl chloride,having a melting point at -97.6 C., is particularly useful, since whenit melts it supplies additional portions of inert diluent. The methylchloride may be the refrigerant as well as the inert diluent and thegrinding solid; or liquid ethylene either in a refrigerating jacket orin admixture with the polymerization reactants, may be used. Similarly,ethyl chloride, having a melting point at -138.7 C., is equallysatisfactorily usable, although in this instance it is its ownrefrigerant; or a refrigerant such as a mixture of liquid methane andliquid ethylene may be used. Similarly, propyl chloride, having amelting point at 11'7 C., may be used. Other useful substances are shownin the following table:

These substances are representative of a considerable number of monoorpoly-halogenatedalkanes which are satisfactory for the purposes of thepresent invention. In addition, solid carbon dioxide is highlyadvantageous, even though 3 it volatllizes and leaves behind no residueto increase the amount of diluent for the formation of a slurry. Also,carbon disulfide having a freezing point at -108 C., is particularlyuseful, as are several of its analogues and homologues.

isoprene or piperylene or dimethallyl (also known It may be noted thatthe solubility relationships between these substances, when liquid, andthe polymer'vary considerably according to the specific substancechosen. Ethyl chloride shows a relatively low solubility for the polymerand markedly promotes the production of a fine grained slurry. Carbondisulfide shows a relatively high solubility for the polymer, and ifpresent in sufficient quantity, maybe caused to yield a substantiallycomplete solution of polymer. starting with the kneader nearly free fromliquid carbon disulfide but filled with solid carbon disulfide, thepolymerization proceeds first under the grinding effect of the solidpolymer, especially if there is a liquid refrigerant having a boilingpoint below the freezing point of the carbon disulfide; then when thepolymerization is nearly complete, and the carbon disulfide begins tomelt,

as diisobutylenyl) or myrcene or the like. These are the preferredpolyolefins but substantially anyof the polyolefins having from 4 to 12or 14 carbon atoms per molecule are useful. The isoolefin is preferablypresent in major proportion and the polyolefin in minor proportion; thebest proportions lying within the range from '70 parts to 99.5 parts ofthe isoolefin with 30 parts to 0.5 part of the polyolefin.

The polymerization is conducted by applying to the olefinic material inthe kneader a Friedel- Crafts catalyst, preferably in solution in a lowfreezing non-complex forming solvent. The preferred catalyst material isaluminum chloride in solution in ethyl or methyl chloride or carbondisulflde. However, substantially any of the Friedel-Crafts catalystsdisclosed by N. 0. Calloway in his article on The Friedel-Craftssynthesis printed in the issue of "Chemical Reviews published for theAmerican Chemical Society at Baltimore in .1935, in volume XVII, No. 3,the article beginning on page 327, the list being particularly wellshown on page 3'75, maybe used. If boron trifiuoride is used, it is ofcourse gaseous and is readily bubbled through the polymerizationmixture. Alternatively, boron trifiuoride and all of the 'othercatalysts may be dissolved in the solvent. For the solvent substantiallyany of the mono or poly alkyl halides which have freezing points below 0C., thereby having low freezing" fluoroalkane, or solid carbon dioxidewith the liquid halogenated fluoroalkane, an excellent emulsion of theolefinic monomer mixture in the liquid fiuorinated alkane may be formed,which is particularly advantageous for polymerization, yielding a linegrained slurry, to an emulsion, of polymer in the fluorinated alkaneliquid. The fact that many of the fluorine containing alkyl compoundshave boiling points above room temperature, and an extremely low solventpower for and solubility in the polymer, permits of a ready separationof the solid polymer from the slurry or emulsion in the fiuorinatedalkane, at room temperature by a relatively simple filtration procedure.In bringing the temperature from polymerization temperature to roomtemperature, practically all of the polymerization mixture substancespresent volatilize away from the polymer substantially completely,leaving behind enough liquid fluorinated alkane to maintain thesuspension, from which the polymer is easily recovered by a filtrationprocedure followed by washing with water for milling at an elevatedtemperature, to remove the last of the liquid material.

For the polymerization procedure, the kneader is cooled to apolymerization temperature ranging from 20 C. down to 164 C., dependingupon the refrigerant used. Solid carbon dioxide sets a temperature of 78C.; solid carbon dioxide in the presence of liquid ethane as arefrigerant sets a temperature of approximately 98 C. Solid carbondioxide in the presence of liquid methane sets a temperature ofapproximately 160 C. To the cold kneader there is then added the desiredpolymerizable olefinic material.

This material preferably consists of isobutylene but in some instancesmay consist of a higher isoolefln such as 2-methyl, butene-l or2-methyl,

pentene-.1 or Z-methyl, hexene-l or the like; in

admixture with a polyolefin such as butadiene or with respect to water,may be used. 'Alternatively, :carbon disulfide and its analogues andhomologues may be used, all of these solvents being characterized bytheir freedom from any tendency to form a complex with theFriedel-Crafts halide, as shown by the fact that the solvent can bevolatilized away from the solute substantially completely without anysignificant change in boiling point. The catalyst is preferablydelivered to the cold polymerization mixture in the form of a fine sprayapplied to the surface of the rapidly stirred material under theinfluence of the kneader blades and the mass of solid refrigerant Whenthe polymerization reaction has reached the desired stage, which may befrom 50% to or even polymerization of the isoolefin and polyolefin, thematerial is removed from the kneader and brought up to room temperature;preferably by dumping the kneader contents into warm water or warmalkali solution or warm alcohol, and the solid polymer is separated fromthe liquid, worked on the hot mill and otherwise purifled as desired.

The material may then be compounded with such substances as sulfur, zincoxide, stearic acid, carbon black and the like and cured at appropriatetemperatures and times.

The resulting polymer shows an excellent tensile strength ranging from1800 pounds to 4500 pounds per square inch; an elongation at break offrom 300% to 1200%; good processing characteristics for such operationsas milling, calendering, extruding and the like; a very desirably lowheat build-up under rapid flexure; ahigh abrasion and flexure resistanceand many other very valuable physical properties. The low heat buildupcharacteristic of this material is well shown in the data chartpresented as a part of Example 1. This low heat build-up shows thespecially valuable properties of this material for use with tires, tubesand the like where heating from rapid flexure is an important item inthe use of the 75 polymer.

EXAMPLE 1 A series of polymerizations were conducted using diflerentamounts of inert diluent and different concentrations of catalyst asshown in Table 1. the amount of methyl chloride being in one instance63.5% of the amount of mixed reactant olefins, and in another the amountof methyl chloride being 167% of the amount of reactant olefins, onepair of polymerizations using 0.35% aluminum chloride solution in methylchloride as catalyst and another pair using 0.69% aluminum chloride inmethyl chloride as catalyst. These several polymerizations wereconducted as follows:

The kneader was cooled by solid CO2 to a temperature well below -60 C.To the kneader there were added 75 parts by weight of solid CO2 asrefrigerant and the kneader was allowed to 0perate until the solidrefrigerant was broken up into small chunks. Approximately parts of amixture of 97% of isobutylene of 98% purity with 3% of isoprene of 96%purity was then added to the kneader with the blades in operation. Therewere then added 16 parts by weight of methyl chloride, and the mixing ofthe material was then conducted in the presence of the methyl chloride.When a thoroughly homogeneous mixture had been obtained, approximately3.0 parts of a catalyst consisting of approximately 0.75% of aluminumchloride in methyl chloride was added through a spray nozzle underpressure to the surface of the reaction mixture, the addition ofcatalyst occupying approximately 6 minutes in time (although in otherinstances the time of addition was varied without change in the reactionbetween 2 minutes and 8 minutes). It was noted that immediately afterthe catalyst addition was begun, the liquid became translucent, forminga milk white suspension of very fine polymer particles. After 2 or 3minutes, the reaction suddenly became much more vigorous, as wasevidenced by a violent bubbling in the mixture (from volatilized CO2),and continued for about 5 minutes after the catalyst injection had beencompleted. The kneader blades were'continued in operation during theentire time of the addition of the catalyst, and for a period ofapproximately 20 minutes thereafter. At the close of this time, thecontents of the-kneader were in the form of a slurry of polymerparticles together with residual quantities of solid carbon dioxide inthe methyl chloride. This liquid slurry was then dumped into warm waterto volatilize out the residual solid CO2 and the methyl chloride, and atthe same time to quench the catalyst. The resulting polymer remained inthe form of a moderately fine grained slurry in the water. It wasreadily separated from the water by a strainer and was then transferredto an open roll mill.

On the mill, the solid polymer was washed with clear water to remove asmuch as possible of the catalyst breakdown product and the alkylationmaterial and was then compounded according to the following recipe:

The compound polymer was then cured in a mold under heat and pressure toobtain a cured specimen which, upon test, showed very interestingproperties.

A comparison of the properties shown by polymer of this type prepared inthe kneader in the absence of diluent and in the kneader in the presenceof diluent is given in the following Table A;

TABLE A Summary sheet of evaluations for diluent and non-diluent kneaderbatch stocks Kneader Batch Diluent Stocks Typical Non-Diluent KneaderBatch Stocks B2.8l Feed, Cata- B-2.8l Feed, Cata- (B-2.93 Feed) lyst.0.85 gm. lyst, 0.69 gm Evaluations A1013 m MeCl AlCh/MeCl (0.325 (0.72(0.635 (1.67 (0.635 (1.67 Cata- Cata- Diluent Diluent Diluent Diluentlyst) lyst) Ratio) Ratio) Ratio) Ratio) Column 1 Column 2 Column 3Column 4 Column 5 Column 6 Yield, Percent by Weight 88. 4 90.3 I 63.369. 3 71. 3 61. 5 Regular Evaluations (60 Cure) pts. carbon black):

57 64 56 72.8 128 154 121 137 Appearance Smooth Smooth Smooth SmoothRebound:

Cure (Min) 40 60 60 60 60 7 at Room Temp. 26.7 126. 7 28. 3 27. 5 27. 827.8 9,; at 0 58.8 58.5 58.8 59.6 Flexometer:

Shore Durometer 56. 6 52. 5 58 59 64 69 Temp. Rise, 0 45. a 56.0 34. 5a2. 5 32.8 as. 7

No'mlz) D iluent ratios referred to in columns 3 to 6 are ratios ofmethyl chloride to isoprene'isobutylene feed,

weight asls.

In this table the first two columns of figures under "non-diluentkneader" show the character of results obtained in the absence of adiluent such as ethyl or methyl chloride; whereas the last four columnsshow the results obtainable with varying the diluent ratios and varyingcatalyst concentrations.

These results show the excellent quality of the polymer as prepared insome of its physical properties.

EXAMPIEZ A polymerization was conducted as in Example 1 except thatafter charging the reactor-kneader with 75 parts by weight of solid CO2there was addedlO parts by weight of a mixture of 95% of isobutylene ofa 98% purity and 5% of isoprene of 96% purity together withapproximately 16 parts by weight of methyl chloride. The polymerizaticnwas conducted as in Example 1 to yield approximately 55% of the reactantolefinic material as a solid polymer. Upon compounding, according torecipes in Example 1, curing and evaluating the cured product, it wasfound to show a substantially higher modulus; approximately 1000 insteadof the 500 to 720 obtained in Example 1. In addition to the highermodulus, this polymer shows a lower heat build-up, a higher rebound,higher tensile strengths, especially when compounded according to thesocalled "pure gum recipe, and a higher Mooney hardness.

EXAMPLE 3 A polymerization was conducted as in Example l but utilizingfor the olefinic reactant material a mixture containing 98.5% ofisobutylene of a 98% purity and 1.5% of isoprene of 96% purity. Thismaterial polymerized equally well and when compounded according to therecipes in Example 1 it cured satisfactorily; also,.the yield was closeto 90% of the reactant olefins. However, the physical properties wereall considerably lower than those shown in the chart in Example 1.

It is well known that the lower the temperature of polymerization, thehigher the molecular weight, and the more satisfactory thepolymerization reaction. Accordingly, a polymerization was conductedusing solid methyl chloride as the refrigerant and grinding material.

In conducting this polymerization, the kneader was cooled by solidmethyl chloride to a temperature well below 90 0. Approximately 50 partsby weight of solid methyl chloride were added to the cold kneader, andapproximately parts by weight of a mixture of 97% of isobutylene of 98%purity with 3% ofisoprene of 96% purity was added to the kneadercontaining a substantial amount of liquid methyl chloride, the amount ofliquid methyl chloride being approximately parts by weight. The reactionwas then continued by the addition of approximately 3 parts by weight ofa catalyst solution consisting of approximately 0.75% of aluminumchloride in methyl chloride, the catalyst being mixed rapidly with theolefinic material in the kneader. The polymerization proceeded rapidlyas in Example 1, a substantial portion of the solid methyl chloridebeing melted by the heat of reaction to yield a more dilute slurry. Theresulting polymer was separated from the slurry, brought up to roomtemperature, compounded according to the recipes in Example 1 andevaluated to yield the following table:

It will be noted that the material is definitely harder, according tothe Mooney plasticity test, that the tensile strength is considerablyhigher, that the modulus is unchanged, the elongation at breakconsiderably increased and the yield approximately the same. It shouldalso be noted that the lower temperature obtainable with solid methylchloride yields an improved rebound, lower heat build-up and betterfiexure and abrasion properties.

It may be noted that carbon dioxide is particularly convenient as anembodiment of this invention because of the fact that it sublimes, andleaves behind no residue; and, in addition, it is non-poisonous and iswithout effect upon the polymerization reaction. The halogenatedalkanes, as above pointed out, are also useful in the reaction eventhough they do not sublime, but merely melt in the course of thereaction, to furnish additional quantities of diluent, therebypermitting the initiation of the reaction with a minimum quantity ofauxiliary diluent, a substantial portion to a major portion of thediluent beliinig provided by the melting of the grinding so It mayfurther be noted that the reaction requires the use of a material whichis solid at the polymerization temperature and which is violatile belowroom temperature, or at a temperature only slightly above roomtemperature, preferably volatile below 100 F. in order to permit of thecomplete removal of the refrigerant and diluent from the polymer withoutthermal injury or overheating of the polymer (although in some instancesthe polymer may be dissolved in a light volatile solvent other than thereaction diluent and precipitated therefrom by alcohol) to insurefreedom from undesired substances such as impurities or residual tracesof the diluent.

The above outlined embodiments of the invention utilize a diluent whichenhances to as great an extent as possible, the production of a slurryof the polymer. However, the reaction proceeds in a somewhat analogousform when other diluents are used. Particularly with carbon disulfidethe polymer is obtained at the end of the reaction in a solution incarbon disulfide. For this embodiment the kneader is prepared as aboveoutlined, cooled with the solid material which may be solid carbondisulfide which freezes at 108.6 C., with or without additional carbondisulfide as diluent. The polymerization mixture, as above outlined, isthen added to the kneader, the kneader put into operation and thecatalyst solution added as above described, The resulting polymer doesnot form a slurry but forms a solution in the carbon disulfide. When thereaction has reached the desired stage (which may be at a point at whichfrom 50% to or even of the polymerizable material is polymerized) thereaction mixture may be dumped into warm water as described, or thereaction mixture may be brought up to room temperature through a heatexchanger and the polymer precipitated from the solution in the carbondisulfide by the addition of a convenient alcohol or glycol, methyl orethyl alcohol or propyl alcohol or ethylene glycol or glycerine or thelike being suitable. In this instance also the powerful grinding andstirring action of the chunks of solid carbon disulfide under the driveof the kneader blade results in a highly advantageous polymerizationreaction to yield a superior polymer.

This reaction proceeds quite well with other homologs of carbondisulfide.

The reaction also proceeds quite satisfactorily with the lowerhydrocarbons. For this purpose such hydrocarbons as heptane, freezing at90.5 C. boiling at +98.5 0., are advantageous. Alternatively, propane,freezing at -189.9 C. or preferably butane freezing at -135 C. or evenbetter, pentane freezing at -131 C. may also be used. These substancesare chilled to the freezing point, and the solid added to the kneader asdescribed for solid carbon dioxide. The polymerization mixture is thenadded to the solid hydrocarbon in the kneader and the polymerization isthen conducted by adding the catalyst as above described. In thisinstance also a slurry is formed which is satisfactory, and theresulting polymer is of excellent quality. However, the polymer shows adefinitely much higher solubility in these hydrocarbons than it does inthe alkyl halides and accordingly the slurry is less grainy in characterand contains much more of the solvent.

As will be obvious from the description in the above examples, theessence of the invention is the polymerization of olefinic material at alow temperature in the presence of an inert diluent and a solid'material which gives a substantial grinding action upon the olefinicmaterial and polymer during the formation of the polymer. Grindingaction is essential to prevent unreacted catalyst from being occluded inpolymer, since occluded catalyst will degenerate the polymer quality.

Thus, the invention provides a polymerization procedure by which thepolymerization is conducted in the presence of a grinding material whichserves simultaneously as a refrigerant, and a diluent to maintain theslurry resulting from the grinding material to yield a slurry of polymerwhich is particularly easy to handle and yields a superior polymer.

While there are above disclosed but a limited number of embodiments ofthe process of the invention, it is possible to produce still otherembodiments without departing from the inventive concept hereindisclosed and it is therefore desired that only such limitations beimposed upon the appended claims as are stated therein or required bythe prior art.

The invention claimed is:

1. A process for the copolymerization of an isoolefinic hydrocarbon of 4to 7 carbon atoms in the molecule with a polyolefinic hydrocarbon of 4to 14 carbon atoms in the molecule which comprises kneading the mixtureof the isoolefin and the polyolefin at a temperature between 20 C. and164 C. in the presence of a Friedel-Crafts catalyst and a chlorofluoroalkane which is solid at the reaction temperature and volatile below F.

2. A process for the copolymerization of a mixture of a major proportionof isobutylene and a minor proportion of isoprene which compriseskneading the mixture of isobutylene and isoprene at a temperature belowl00 C. in the presence of solid dichlorotetrafluoroethane and a Friedel-Crafts catalyst.

3. A process for the copolymerization of a mixture of a major proportionof isobutylene and a minor proportion of isoprene which compriseskneading the mixture of isobutylene and isoprene at a temperature belowC. in the presence of solid dichlorodifluoromethane and a Friedel-Crafts catalyst.

4. A process for the copolymerization of a mixture of 97% isobutyleneand 3% isoprene which comprises kneading the mixture of isobutylene andisoprene at a temperature below 100 C. in the presence of soliddichlorotetrafiuoroethane and aluminum chloride dissolved in an organicsolvent which does not form a complex with said aluminum chloride.

JOHN S. SAYLOR, JR.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,243,470 Morway May 27, 19412,276,893 Thomas Mar. 17, 1942 FOREIGN PATENTS Number Country Date543,420 Great Britain Feb. 25, 1942

1. A PROCESS FOR THE COPOLYMERIZATION OF AN ISOOLEFINIC HYDROCARBON OF 4TO 7 CARBON ATOMS IN THE MOLECULE WITH A POLYOLEFINIC HYDROCARBON OF 4TO 14 CARBON ATOMS IN THE MOLECULE WHICH COMPRISES KNEADING THE MIXTUREOF THE ISOOLEFIN AND THE POLYOLEFIN AT A TEMPERATURE BETWEEN -20*C. AND-164*C. IN THE PRESENCE OF A FRIEDEL-CRAFTS CATALYST AND A CHLOROFLUORALKANE WHICH IS SOLID AT THE REACTION TEMPERATURE AND VOLATILE BELOW100*F.